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Journal of Engineering Science and Technology Vol. 10, No. 4 (2015) 485 - 495 © School of Engineering, Taylor’s University

485

EFFECT OF LDPE RAW MATERIAL ON STRENGTH, CORROSION AND SORPTIVITY OF CONCRETE

R. MANIKANDRAN, D. S. NIRMALA, G. DHINAKARAN*

School of Civil Engineering, SASTRA University, Thanjavur 613401 Tamil Nadu, India

*Corresponding Author: [email protected]

Abstract

Many researchers focused on effect of Low Density Poly Ethylene (LDPE) on bituminous pavements or concrete to modify the strength and ductility in view of reusing the abundant quantity of non-degradable LDPE material available. It also reduces the use of bituminous materials and disposal problems of such waste material. Developing countries are moving towards construction concrete pavement or converting bituminous pavements into concrete pavements. Hence in this paper an attempt has been made to study the feasibility of using LDPE raw material itself as a modifier in cement concrete with a characteristic compressive strength of 20 MPa. Present study focuses on effect of addition of LDPE raw material (3, 4 and 5%) under different temperatures (70°C, 80°C and 90°C) and duration of thermal curing (4, 8 and 16 hours) on compressive strength, corrosion resistance and sorptivity. It was inferred from the results that, addition of LDPE raw material considerably increases the compressive strength, resistance against corrosion and permeability. Results also revealed that concrete with 3% LDPE modifier for 80°C with 4 hours of thermal curing was found to be optimum.

Keywords: LDPE, Compressive strength, Sorptivity, Corrosion resistance, Thermal curing.

1. Introduction

Locally available cement concrete is a better substitute to bitumen, which is the by-product in distillation of imported petroleum crude. Within two to three decades bituminous pavement would be a history and thus an alternative is very essential. Some of the solutions would be use of polymer fibre, crumb rubber modifier, recycled plastics, waste plastics and raw materials of plastics in concrete

486 R. Manikandan et al.

Journal of Engineering Science and Technology April 2015, Vol. 10(4)

Nomenclatures A Area of cross section of specimen, mm2 Q Quantity of water absorbed under capillary suction, mm3 t Time interval of observation, s

pavements. Polymer has several advantages like longer life, low maintenance cost, good riding quality, increased load carrying capacity and impermeability to water over flexible pavements. It accomplishes improved durability and also helps to achieve reduced bleeding of water to surface during concrete placement, which inhibits migration of cement and sand to the surface and benefits of the above will be harder, more durable surface with better abrasion resistance.

From the literature it was understood that numerous research woks were carried out in the area of replacing natural aggregate partially with waste materials in the form of construction and demolition waste [1], glass [2-5] and polymers [6-8]. A review of the literature has revealed that more works related to construction and demolition waste and glass were performed than that of polymer waste. It was inferred from the results of their research that replacement of natural aggregate with either construction and demolition waste or glass reduced the compressive strength of resulting concrete and also found that there was more amount of water absorption in concrete. In addition generation of alkali–silica reaction gel remains a major concern for glass modified concrete [9]. In the case of polymers, a good amount of recyclable polymers formed a huge landfill due to the low cost of producing them from virgin material, mixing of polymer types during recycling, or contamination with other materials [10].

Study on effects of replacement of fine aggregate with polymer aggregate was performed and found that considerable amount of reduction was observed in density, i.e., 20% sand replacement with waste polyethylene and polystyrene aggregate yielded 7% reduction in the density of the concrete[11].

Potential use of pyrolysis low density polyethylene (LDPE) as a modifier for asphalt paving materials was investigated and results indicated that modified binders showed higher softening point, keeping the values of ductility at minimum range of specification of (100+ cm), and caused a reduction in percentage loss of weight due to heat and air [12]

LDPE as a modifier for asphalt paving materials was studied and found that optimum requirement of PE was 2.5%. They also found that Marshall Stability, resilient modulus, fatigue life, and moisture susceptibility of mixes were improved as a result of modification of asphalt cement by reclaimed polyethylene [13].

Experiments were conducted on the use of reclaimed polyethylene (PE) obtained from low-density polyethylene (LDPE) carry bags, a locally available low-cost waste material collected from garbage, for modification of (80/100)-grade asphalt. They evaluated engineering properties by conducting beam test and found that the flexural stiffness of the PE-modified mixtures were found to be comparatively higher than the conventional mixtures. They also found that fatigue life of the PE-modified mixtures increased by 2.5 times when compared to conventional mixtures [14].

Effect of LDPE Raw Material on Strength, Corrosion and Sorptivity of Concrete 487


Hence in the present paper the effect of LDPE raw material as a modifier in three different percentages with different magnitudes of temperature and duration of thermal curing on compressive strength, corrosion resistance and resistance to capillary suction (sorptivity) of concrete is studied.

2. Experimental Investigation

2.1. Materials used

The cement used for the study was Ordinary Portland Cement of ASTM Type 1. The specific gravity of the cement was to be 3.15. The Coarse Aggregate used was broken stone. The Specific Gravity and Water absorption of broken stone are 2.76 and 0.78 % respectively. Size of coarse aggregate used here was 20 mm downsize. The fine aggregate used was river sand. The Specific Gravity of river sand is 2.67. LDPE used in the present work was 3 mm sized balls with a trade name of 1005FY20 supplied by Reliance Polymers (Fig.1) and density was 9.2 kN/m3. An immersion water heater attached with thermostat was used for thermal curing. Thermostat is a device that automatically controls heating in such a way as to maintain a temperature at a constant level. This setup was designed in such a way that, when the temperature of water reaches the desired value, the thermostat automatically will be switched off and when the temperature falls down below the desired value it will be switched on.

Fig. 1. Appearance of LDPE raw material.

2.2. Methodology

Specimens were cast and tested with different percentages of LDPE to study the effect of LDPE, different magnitudes of temperature to study the effect of temperature, different duration of thermal curing to arrive the optimum duration and different medium to study the resistance against sulphate and acid attack. The Mix proportion arrived was 1:1.47:3.32 to get a characteristic compressive strength of 20 MPa. The water cement ratio adopted was 0.48 which was obtained from the Slump Cone test. Concrete cubes of size 150 mm × 150 mm × 150 mm



were cast for different combinations of concrete with 3, 4 and 5% of LDPE modifier. Curing was done for normal temperature and for 70°C, 80°C and 90°C to study the effect of curing temperature on LDPE modified concrete. Effect of curing duration also was studied by varying duration of curing as 4 hours, 8 hours and 16 hours. Compressive strength test were conducted for control concrete and LDPE modified concrete (Fig. 2).

Fig. 2. LDPE raw material modified concrete under compression test.

Then short term durability property in terms of sorptivity and resistance to corrosion were also performed. The durability of concrete structures is closely related to the nature and severity of the environment in which they are located, as well as the nature of the concrete construction. To assess the effect of addition of LDPE modifier on resistance against acid and sulphate attack the following procedure was adopted. After the specimens were subjected to 4 hours thermal curing with a constant temperature of 80°C and 28 days curing in normal water, they were further cured in a tank which contains hydrochloric acid with 0.01N to study the resistance of concrete cubes against acid attack. Similarly other set of specimens were immersed in a tank which contains sulphuric acid with 0.01N to study the resistance of concrete cubes against sulphate attack. After 28 days of curing in acid and sulphate solution, they were taken out for testing for its compressive strength to assess the extent of corrosion damage.

Surface sorptivity is the measurable parameter which indicates the degree of water absorbency or permittivity under capillary suction. Surface Sorption coefficient was also arrived from the observed values of the experiments. Concrete cylindrical specimens of 3 each for control, 3%, 4%, 5% LDPE modified concrete with a water-cement ratio of 0.48 were cast in standard sorptivity moulds of dimensions of 102 mm diameter and 50 mm height as per ASTM C1585-13 [15]. The specimens were cured for a time period of seven days. The specimens were then kept for air drying for a period of one day. The bottom and circumferential portions of the air dried specimen were sealed tightly by using several layers of adhesive tape to prevent the entry of water on to the cylinder through the sealed regions. The initial mass of the specimens were



observed and the top portion, i.e., the unsealed portion of the specimens was exposed to water depth of about 2-3 mm. The mass of the specimens were observed for specific periods of time interval. The mass after the specified time intervals were observed after the removal of surface moisture. The differences in mass were used to plot a graph between Q/A versus √t, the slope of the graph obtained is the coefficient of surface sorption. The coefficient obtained from the graph advocates for determination of durability.

2.3. Details of specimen

Concrete cubes were cast and tested for its compressive strength, sorptivity and corrosion. Control concrete cube specimens of 150 mm x 150 mm x 150 mm were cast and kept in normal water curing for 28 days. The specimens were cast with the following combinations. First set of specimens were cast by adding LDPE with 3, 4 and 5% for 4 hours thermal curing at 70, 80, and 90°C respectively including control concrete .This procedure is repeated for 8 and 16 hours of thermal curing for remaining set of specimens. Hence in total, there were 108 specimens of concrete cubes were cast. Corrosion test was done by immersing cube specimens in HCl and H2SO4 Solution with 0.01 N for 28 days. Concrete cylindrical specimens of 100 mm diameter and 50 mm height of 3 specimens in each category of Control, 3%, 4% and 5% LDPE modifier mixed concrete were cast in Standard Sorptivity mould. Then corresponding Sorptivity test was performed.

3. Results and Discussion

3.1. Compressive strength

3.1.1. Effect of LDPE modifier in thermal curing

LDPE raw material was added with 3, 4 and 5 % of cement by weight to understand its effect on compressive strength under thermal curing. Specimens cast with LDPE modifier were not subjected to normal curing due to the fact that sufficient bonding between LDPE modifier and other ingredients not developed. In a similar way percentage of LDPE modifier was limited to 5% because of low density (light weight) it occupied more volume and created problem while preparing fresh concrete. Hence the specimens were subjected to thermal curing. By keeping the melting point of LDPE modifier in mind, the magnitudes of temperature were selected as 70°C, 80°C and 90°C. Figures 3 to 5 depict the results on compressive strength of LDPE modified concrete under thermal curing for different duration. It was understood that compressive strength increased due to the addition of LDPE modifier when compared to control concrete irrespective of magnitude and duration of thermal curing. Increase in LDPE modifier percentage was directly proportional to increase in strength. Addition of 3% LDPE modifier increases compressive strength to an extent of 10 to 14 % for 4 hours duration of curing, 2 to 10% for 8 hours duration of curing and 5 to 24 % for 16 hours duration of curing for different temperatures. These values for 4% LDPE modified concrete were observed as 20 to 30 %, 12 to 20 % and 22 to 30 % for 4, 8 and 16 hours duration of curing respectively for different temperatures.



Similarly these values for 5% LDPE modified concrete were observed as 35 to 44 %, 22 to 30 % and 33 to 40 % for 4, 8 and 16 hours duration of curing respectively for different temperatures. Though there was linear trend in increase in compressive strength due to increase in temperature, the rate increase of compressive strength with respect to control concrete was not linear due to magnitude of compressive strength gained by control concrete. It was due to reason that addition of LDPE modifier was very much effected during the initial period of thermal curing and further extension of its magnitude not very much significant. It was also to be remembered that accelerated curing of control concrete made rate of increase of compressive strength of LDPE modified concrete for longer duration as insignificant. Among the results of LDPE modified concrete considering the effect of LDPE modifier, concrete with 5% addition yielded better results in terms rate of increase of compressive strength with respect to control concrete. Minimum compressive strength for 5% LDPE modified concrete was 33 MPa and the maximum value observed was 45 MPa.

Fig. 3. Compressive strength of LDPE modified concrete for 4 h curing.





3.1.2. Effect of magnitude of thermal curing

Figures 3 to 5 depict the variation of compressive strength of LDPE modified concrete with respect to curing under various temperatures. The results revealed that increase in magnitude of curing increased the compressive strength irrespective of duration of thermal curing and percentage of LDPE modifier. For all the temperatures, rate of increase of compressive strength with 3% LDPE modified concrete with respect to control concrete was found to be less compared to other two percentages. For majority of combinations increase of temperature from 70°C to 80°C yielded better rate of increase of compressive strength of concrete and it might be due to reason that 80°C made LDPE modifier to uniformly distributing into the voids by completely filling it and also found to be an optimum temperature. A temperature of 70°C might be little bit inadequate in terms of melting the LDPE modifier available into concrete especially failed to reach core part of concrete. It was efficient to certain extent only and hence lesser rate of increase of strength was observed for 70°C. Likewise for a temperature of 90°C flow ability might be on the higher side than required and uniform distribution of LDPE modifier might not be there. Of course in some cases the results were in the mixed bag for which other parameters like differences in compaction and distribution of aggregates might also be the reasons.

3.1.3. Effect of duration of thermal curing

The variation of compressive strength of LDPE modified due to the effect of duration of thermal curing is depicted in Figs. 3 to 5. Considering the effect of duration of thermal curing higher rate of increase of compressive strength for LDPE modified concrete was observed with respect to control concrete. For a particular duration of thermal curing, effect of temperature was less pronounced for control concrete on compressive strength. It means that effect of temperature differential of 20°C (i.e., from 70°C to 90°C) does not make any phenomenal difference in control concrete due to its conventional composition. However when LDPE modifier was added with concrete increase of temperature made differences in microstructure of concrete by making the polymer material to serve



as ductile material during thermal curing, filling the voids and subsequently hardening over period of regular curing period. Higher magnitudes and rate of increase of compressive strength values were found for LDPE modified concrete especially for the concrete with 4 and 5% addition of LDPE modifier for a period of 4 hours and 16 hours of thermal curing. Though there was an increase in compressive strength under the duration of 8 hours of thermal curing the rate of increase was marginal except for concrete with 5% LDPE modifier.

From the results of compressive strength it was found that concrete with 5% LDPE modifier yielded higher rate of increase of compressive strength over control concrete for all the temperatures and duration of thermal curing. Though there was higher rate of increase was found in 16 hours of thermal curing, concrete with 4 hours of thermal curing were subjected to rapid gain in compressive strength in short period. In a similar way among three different temperatures tested 80°C yielded better results. By considering the economy without compromising the strength 4 hours and 80°C were taken as an optimum duration and temperature for thermal curing of LDPE modified concrete. For specimens to be tested for its resistance against corrosion they were cast for this optimum values only.

3.2. Resistance against corrosion

From the results of corrosion test shown in Fig. 6, it was understood that concrete with 3% LDPE modifier has yielded better resistance against both acid and sulphate attack among all the specimens. For 3% LDPE modified concrete, the rate of increase of compressive strength with respect to control concrete in HCL solution it was about 15% and H2SO4 solution it was about 17%. For 4% LDPE modified concrete, there was a reduction in compressive strength with respect to control concrete in HCL solution and it was about 1.2% and in H2SO4 solution the strength has increase to a value of 13% than control concrete. Further increase of LDPE modifier to 5% showed a reverse trend both in HCl and H2SO4 solutions. The compressive strengths were reduced to an extent of 9% in both the cases with respect to control concrete. The results of compressive strength of LDPE modified concrete in HCl and H2SO4 solutions revealed that concrete with 3% LDPE was found to be optimum percentage in terms resistance against corrosion.

Fig. 6. Strength of LDPE modified concrete for HCl and H2SO4 curing.



3.3 Evaluation of Sorptivity Characteristics

Table 1 gives the details of the amount of penetration or absorption of water into the various samples with respect to increase in time. The readings were taken at various time intervals as per ASTM C1585-13 [15] and were represented in seconds. The mass of the various samples were recorded at all the stipulated times and the change in mass of the sample with respect to its initial oven dried mass is calculated. This increase in mass observed represents the water absorption of the sample and the same was represented in terms of volume of water ingress through the bottom surface, i.e., as flow (Q) in mm3.The penetration depth (mm) for each

Table 1. Sorptivity results of control and LDPE modified concrete.

Time

‘t’ in

s

Square

root of

time

in s1/2

Q in mm3 Area (A)

in

mm2

Sorptivity in mm

LDPE modifier LDPE modifier

0% 3% 4% 5% 0% 3% 4% 5%

0 0 0 0 0 0 7854 0 0 0 0

60 7.75 1710 1220 2940 3670 7854 0.22 0.16 0.37 0.47

120 10.95 1960 1710 3430 4160 7854 0.25 0.22 0.44 0.53

240 15.49 2210 1960 3670 4410 7854 0.28 0.25 0.47 0.56

480 21.91 2450 2210 4410 5140 7854 0.31 0.28 0.56 0.65

960 30.98 2940 2690 5140 5870 7854 0.37 0.34 0.65 0.75

1920 43.82 3430 3120 6360 7090 7854 0.44 0.40 0.81 0.90

3840 60.00 4410 4160 7220 7340 7854 0.56 0.53 0.92 0.93

7680 87.63 5380 4160 6610 7340 7854 0.69 0.53 0.84 0.93

15360 123.94 6180 5010 6360 7710 7854 0.79 0.64 0.81 0.98

of the sample at every single time interval was determined by dividing the flow with surface area exposed to absorption.

The water absorbed by capillary suction with respect to increasing time was observed to follow an increasing trend and for some cases it was constant. Form the results shown in Table 1 it was understood that with an increase in amount of LDPE modifier, the sorptivity values varied distinctively. For 3% LDPE modifier the values of sorptivity were very less compared to all the specimens. Further increase of LDPE modifier to 4 and 5% decreased the resistance against capillary suction and might be due to improper filling of voids. The sorptivity values of 4 and 5% of LDPE modified concrete were found to be more than the values of control concrete. The sorptivity values for 3% modified concrete were found to be less among all the mixes. It is also to be noted from the results corrosion results that, concrete with 3% LDPE modified concrete yielded better resistance. Hence concrete with 3% LDPE modifier was found to be optimum in terms of compressive strength, resistance against capillary suction and resistance against corrosion.



4. Conclusions

From the detailed investigations carried out on LDPE modified concrete to study the effect of thermal curing for its compressive strength, sorptivity and resistance against corrosion following conclusions were arrived:

• LDPE modified concrete was very effective in improving compressive strength in thermal curing. Almost for all percentages of LDPE modifier the compressive strength was higher than the control concrete and concrete with 5% LDPE modifier yielded maximum compressive strength and could be made use of in the field where durability was not the prime factor.

• Considering the effect of corrosion resistance, concrete with 3% LDPE modifier was found to be an optimum percentage and further increase of LDPE modifier showed a reverse trend due to heterogeneity of concrete with increased volume.

• Similar trend as observed in resistance to corrosion found to be same for short term durability criteria called sorptivity also. Concrete with 3% LDPE modifier yielded better resistance against capillary suction.

• In terms of strength and durability criteria concrete with 3% LDPE modifier was found to be an optimum percentage of addition when concrete subjected to thermal curing for an optimum temperature of 80°C for the curing duration of 4 hours. Though we get similar results for 16 hours curing, considering the economy and practical difficulties the above optimum values were suggested.

Acknowledgement

The authors would like to thank the Vice Chancellor of SASTRA UNIVERSITY for having provided experimental facilities in the School of Civil Engineering to do this research work and also for the continuous support and encouragement given throughout this research work.

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